Cu wire development for thin QFN package using die attach film (DAF)

The drive for package miniaturization and die thickness reduction has created new challenges for conventional die attach paste materials. Die attach film (DAF) is seen as a candidate in package of thin QFN. A reliability test was performed respectively on HAST (130°C/85%) and HAST (110°C/85%) JESD22-A101/A110 for thin QFN. The lift ball failure was happened in response to HAST (130° C/85%), the failure mechanism was confirmed due to bond pad corrosion that IMC (intermetallic compound) was corroded by chloride under high humidity with bias. Contrary to HAST (110´ C/85%), there were no failure and MC degradation. Hence, HAST temperature effect in relation to product application is crucial to decide HAST condition. The extracted ions were analyzed by ion chromatography and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) when temperature above 120 deg C chloride ion was leached. That contributed to reliability risk on Cu wire package under humidity environment. Apart from DAF extraction test, a TGA (Thermogravimetry analysis) was performed before and after curing. There was no significant change when temperature was within 200 deg C under dry condition. In summary, this study discloses how chloride ion attached and corroded bond pad at high temperature 130 deg C as result of ball lift and the concentration of chloride on DAF assembled in IC package in relation to selection of HAST condition at 110 deg C without failure with positive ball shear and no IMC degradation to safeguard reliability test.